Capacitive touchscreen displays, for example those present in smart phones, rely on the electrical properties of the human body to detect when and where on a display the user is touching. Because of this, capacitive displays can be controlled with very light touches of a finger and generally cannot be used with a mechanical stylus or a gloved hand. For a capacitive device, the capacitive screen is made of an insulating layer that can also be transparent, such as glass or plastic. If the insulating layer is transparent, then a thin trace of transparent conductive material is used to form electrical patterns on the inside of the insulating layer. When a user touches the monitor with his finger, some of the charge is transferred to the user, so the charge on the capacitive layer decreases. This decrease is measured in circuits located at each corner of the monitor. The computer calculates, from the relative differences in charge at each corner, exactly where the touch event took place and then relays that information to the touch-screen driver software.
Flexible electronics, also known as flexible circuits, result from assembling electronic circuits by mounting electronic devices on flexible substrates. The flexibility of the circuit is typically limited not only by the flexibility of the substrate, but also by the flexibility of the electronic devices, circuit lines and interconnections mounted on the substrate.
Conductive layers, circuit wiring and interconnections can be formed using a conductive paste, typically comprising conductive particles dispersed in an organic medium. Existing conductive pastes are not suitable for selective structuring at the micron-sized level, as required, for example, in microelectronics manufacture. In addition, such pastes do not exhibit adequate resistance to environmental effects such as, for example, extremes of temperature. Conventional conductive pastes may comprise an epoxy resin. In such pastes, the hardening agent is flaky and hard, a therefore the pastes are not suitable for manufacturing flexible circuits. The electrically conductive pastes are also prone to form a gel after being kept in storage for a long time. Other conventional polymeric pastes have the disadvantage of non-flexibility. As a result, a functional circuit made of conventional electrically conductive paste is likely to crack. Conventional conductive pastes, such as, for example, those containing silver nanoparticles or metal complex particles cannot typically be sintered at low temperature. Accordingly, when a circuit or conductive layer or interconnection is formed on a substrate using such conventional pastes, damage to the substrate may occur.
There is a need for a conductive paste capable of forming a flexible conductive layer, circuit wire and/or interconnection at low temperature, which is capable of being stretched without substantial crack formation or substantial loss in electrical continuity. There is also a need to make solderable flexible paste for applications such as, for example, decorative LED lighting.
The present invention seeks to tackle at least some of the problems associated with the prior art or at least to provide a commercially acceptable alternative solution thereto.
The present invention provides a conductive paste comprising conductive particles dispersed in an organic medium, the organic medium comprising:                a solvent; and        a binder comprising a polyester.        
Each aspect or embodiment as defined herein may be combined with any other aspect(s) or embodiment(s) unless clearly indicated to the contrary. In particular, any features indicated as being preferred or advantageous may be combined with any other feature indicated as being preferred or advantageous.